Random review:
“Tux Paint is our 3-year-old son's favorite activity. It's been an amazing creative outlet for him--he loves to make up stories while he draws. We've been impressed at how intuitive and fun it has been for him.”
— Ashley L.

Download - Apple iOS (iPhone, iPod Touch, iPad)

Tux Paint for iOS (iPhone, iPod Touch, iPad) (Unofficial)

A 3rd party has ported Tux Paint to iOS, and released an 'App' for Apple iPhones, iPod Touches, and iPads. It is available for free in the App Store as "Tux Paint Free". (This version is not officially supported by the Tux Paint developers, though the developer is participating in the project.)

Compatibility note: The current version of Tux Paint requires iOS version 6.0 or later. (A version for iOS 4.3, for iPad only, is available for USD $1.99, Tux Paint HD.)